Research On Solid State Wide Bandwidth Terahertz Multiplier Source And Mixer Detector

Terahertz(THz)has the features of the low quantum energy,wide-bandwidth,better capability of penetrating the non-polar materials,etc,which lies between the millimeter wave and the infrared.THz technology can be widely applied in radar,communications,medical,radio astronomy,space exploration,and security detection,etc.,which has been considerrred as one of the ten most valuable technologies to change the world in the future.Two major methods usually can be used to generate and receive the THz signals including the optical and electrical methods,which are the key to the scientific researches and engineering applications in THz.Due to the advantages such as small size,and tunable frequency,the solid THz signals generated and received based on the frequency multiplying and mixing methods have caused wide attentions in the field of THz.With the development of the semiconductor technology,the performances of THz multiplier sources and mixer detectors have made great advances.However,how to solve the problems including the inter-constraint between the wide-bandwidth and the higher efficiency,and the achievement of the multiplier and mixer with higher efficiency and wide-bandwidth still faces some chanllenges and difficulties.To meet the requirements of measurement with higher sensitivity,larger dynamic range and higher power,this paper mainly conducted the model of the THz planar Schottky diodeg,wideband and higher efficiency multiplying,broadband and lower conversion loss even harmonic mixing,wideband chains of multiplying and mixing,etc,around solid wideband THz multipliers and mixers.The innovative technologies of multi-layer space multipling,no medium multipling,distributed multi-point grounded broadband mixing,etc are proposed in this paper.The contributions of the paper can be summarized as:1.Due to the higher frequency of the THz conversion circuit,and higher requirements of nonlinear device model,a method of parameters extraction is developed based on the influence of the nolinear parameter port impedance,which can achieve the equivalent parasitic parameters in the 3D device model.Furthermore,the circuit can be continuously modified based on the acquired measurements to enhance the accuracy.Using the above model,an integrative and precise full-field simulation method is developed to design the THz frequency conversion circuit,which takes the error components such as substrate fabrication,waveguide fabrication,diode and cavity assembly into account to reduce the assembly process requirements of micro-size THz Circuit Hybrid integration.It can better achieve the hybrid integration of micro-size THz circuits and solve the accurate design problem for frequency conversion circuit in a wide bandwidth.2.A design algorithm of the doubler without dielectric material is developed in this section.And the circuit model of the doubler is designed which contains metal fin lines and a balun.The balun,which feeds the input signals to T-type diodes with equal amplitude and opposite phase,is formed by the slot line and the gradual metal ridge that is perpendicular to the wide side of the input waveguide.To achieve the better performance of the wideband,the gradual property of the metal ridge meets the n-order sine and the exponential functions.Then,the second harmonics can be acquired based on the metal fin lines.To make the second harmonics transmitting to the output ports,an air-bridge across the ridge is employed.Compared with the conventional doublers,the proposed designer without substrate can eliminate the dielectric loss,substrate parasitic,enhance the efficiency,and extend the bandwidth.A wideband doubler is fabricated and measured,which can achieve a higher efficiency within 8.7%~12.7% in the range of 140~220 GHz.The acquired results can better fit well with the simulation results.3.The Monolithic Microwave Integrated Circuit(MMIC)is researched in this section based on the thin film process.The doubler model in the range of 170~260 GHz is designed based on the waveguide and microstrip probe.The waveguide and microstrip probes are employed as the balance and unbalance structures in the designed doubler model.A I-type fundamental filter unit with higher Q values is used to reduce the influences of the fundamental signals spurious on the doubler circuits,whih can achieve better coupling properties between the series diodes and the input signals in the range of 85~130 GHz.The 3D electromagnetic field model of T-type diode is established.The integrative impedance matching is designed with the diodes,output waveguides and the probes together.The higher coupling outputs of the signals in the range of 170~260 GHz at the diode anode are achieved,the bandwidth is expanded,and the efficiency of the doubler is improved.To verify the mechanism above,the 170~260 GHz doubler is fabricated and measured,which shows better performance with the efficiency more than 4% and the typical output power larger than 2 mW in the whole operational band.The acquired results can better fit well with the simulation results.4.The spatial multi-layer multiplier method is proposed in this section based on the spatial power combining,and a tripler model in the range of 110~170 GHz is introduced.The spatial multi-layer metal fin-line structure is used in the designed model,which can effectively improve the compression point of the tripler and eliminate the dielectric loss.The good symmetry of the ridge waveguide is used to eliminate the phase effect caused by the physical length of the nonlinear device,and improve the spurious suppression.In addition,the devices directly interconnected to the cavity,whih can improve the heat dissipation efficiency of the device and ensure the reliability of the tripler.Finally,the fabrication,assembly and test of the 110~170 GHz double-layer tripler are completed.Driven by 147~208 mW input power,the circuit has a full bandwidth efficiency of 5.7%~7.8% and a power with standing capacity of more than 0.5 W.The acquired results can better fit well with the simulation results.5.An approach is developed to design the even-order-harmonic mixer based on a pair of anti-parallel schottky diodes in this section.To implement the approach,a wideband model of the even-order-harmonic mixer is designed with the distributed multipoint grounding.Two shorted grounds at the radio frequecny(RF)port are employed,which can improve the coupling efficiency of the RF,and effectively suppress the influences of the mixing products on the working state of the device.That realizes the broadband impedance matching and further expands the bandwidth of the RF signals.Series LO(Local oscillator)LPF(Lowpass filter,LPF)with high Q suspended microstrip resonant unit is used to suppress the harmonics of the LO and to eliminate the influences on the wideband performance of the mixer.The LO LPF can also reduce the leakage of the RF signals to LO port to improve the isolation between the RF and the LO ports.To verify the mechanisms above,a wideband fourth-harmonic operating at 325~500 GHz and a wideband subharmonic mixer at 260~400 GHz are fabricated and measured,respectively.The proposed mixers has merits of the low conversion loss of 15~22 dB in the range of 325~500 GHz and 10~14 dB in the range of 260~400 GHz.The acquired results can better fit well with the simulation results.6.A 325~500 GHz multiplier chain and mixer chain is proposed.The multipling factor of the multiplier chain,which consists of a 18~28 GHz doubler,a 36~56 GHz doubler,a 36~56 GHz power amplifier,a 108~166 GHz tripler,and a 325~500 GHz tripler,is ×36.The mixer chain adopts a fourth-harmonic mixer with a ×6 LO chain,which consists of a 27~41.7 GHz multiplier amplifier and a 81.3~125 GHz tripler.To verify mechanisms above,each module of the multiplier chain and mixer chain is fabricated and measured.The measured results indicate that the output power of the multiplier chain is more the-10 dBm and the conversion loss of the mixer chain is from 15~ 22 dB.